Progressive Enhancement in 2 minutes

Wikipedia states that Progressive Enhancement principle:

uses web technologies in a layered fashion that allows everyone to access the basic content and functionality of a web page, using any browser or Internet connection, while also providing those with better bandwidth or more advanced browser software an enhanced version of the page

This is the best example I have found of how Progressive Enhancement is applied:

This is serverfault.com and site still works without JavaScript. However they politely inform that if I enable JavaScript, the site will work better (See the red bar in the top “Server Fault works best with JavaScript enabled”).

In other words, don’t discriminate visitor because of the browser they use, be polite and at least provide some functionality.